1. Field of the Invention
This invention relates to process control systems. More specifically, the present invention relates to a process control system which monitors and uniformly displays diagnostic information of devices of multiple different types.
2. Description of the Related Art
Present-day process control systems use instruments, control devices and communication systems to monitor and manipulate control elements, such as valves and switches, to maintain at selected target values one or more process variables, including temperature, pressure, flow and the like. The process variables are selected and controlled to achieve a desired process objective, such as attaining the safe and efficient operation of machines and equipment utilized in the process. Process control systems have widespread application in the automation of industrial processes such as the processes used in chemical, petroleum, and manufacturing industries, for example.
Control of the process is often implemented using microprocessor-based controllers, computers or workstations which monitor the process by sending and receiving commands and data to hardware devices to control either a particular aspect of the process or the entire process as a whole. The specific process control functions that are implemented by software programs in these microprocessors, computers or workstations may be individually designed, modified or changed through programming while requiring no modifications to the hardware. For example, an engineer might cause a program to be written to have the controller read a fluid level from a level sensor in a tank, compare the tank level with a predetermined desired level, and then open or close a feed valve based on whether the read level was lower or higher than the predetermined, desired level. The parameters are easily changed by displaying a selected view of the process and then by modifying the program using the selected view. The engineer typically would change parameters by displaying and modifying an engineer's view of the process.
In addition to executing control processes, software programs also monitor and display a view of the processes, providing feedback in the form of an operator's display or view regarding the status of particular processes. The monitoring software programs also signal an alarm when a problem occurs. Some programs display instructions or suggestions to an operator when a problem occurs. The operator who is responsible for the control process needs to view the process from his point of view. A display or console is typically provided as the interface between the microprocessor based controller or computer performing the process control function and the operator and also between the programmer or engineer and the microprocessor based controller or computer performing the process control function.
Diagnostic information is one type of information that is useful to monitor and display in a process control system. However with the various types of devices in a process control system, including a wide variety of field devices, diagnostic information is not generally monitored in a consistent manner from one device to the next. Furthermore, important diagnostic information typically relates to the interaction of multiple portions of the control system, for example, the combined operations of a controller and device or multiple devices and controllers. Diagnostic information relating to multiple circuits in a system is typically not handled by existing process control systems.
Diagnostic information is most useful when related to the various control operations that are occurring when the diagnostic information is monitored. Conventional process control systems typically access and display diagnostic information with no relation to the control operations or control schemes that are functioning during diagnostic testing.
One problem associated with the use of graphical views for diagnostic displays is that existing systems allow only the equipment manufacturer, not a user of this equipment, to define the diagnostic information to be monitored, along with associated graphical views, or modify the predefined diagnostic functions within the provided library.
What is needed is a uniform or universal design environment that can easily be used, not only by a designer or manufacturer but also a user, to customize monitoring and display of diagnostic operations for a variable number and type of devices and components of a process control system. What is further needed is a personal computer-based process control system that includes a flexible diagnostic monitoring and display functionality that is easily implemented within substantially any size process and which is updated by users, without the aid of the control system designer, to monitor and display diagnostic information for various combinations of process field devices.